1. Field of the Invention
The present invention relates to a multi-cylinder piston type compressor, such as a multi-cylinder swash-plate type compressor or a multi-cylinder wobble-plate type compressor adapted for use in compressing a refrigerant gas of an air-conditioning system, e.g., a car air-conditioning system. More particularly, it relates to a pulsation and noise suppression means accommodated inside the multi-cylinder piston type compressor.
2. Description of the Related Art
U.S. Pat. No. 4,534,710 of Higuchi et al discloses a typical multi-cylinder swash-plate type compressor for use in automobile air-conditioning systems. The conventional compressor has an axially extending cylinder block in which a multi-cylinder piston type compressing system operated by a single rotary swash plate is contained. The front and rear ends of the cylinder block are closed by front and rear housings in which suction and discharge chambers for a refrigerant gas are arranged.
The refrigerant gas returning from the air-conditioning system is drawn into the suction chambers of the front and rear housings, and subsequently introduced into the cylinder bores in which the refrigerant gas is compressed by the reciprocating motion of the pistons. The compressed refrigerant gas is then pumped out of the cylinder bores into the discharge chambers of the front and rear housings. The conventional compressor is also provided with a valve plate arranged between each of the front and rear ends of the cylinder block and the front or rear housing. The valve plate has a plurality of suction ports allowing communication between the suction chamber and the cylinder bores and a plurality of discharge ports allowing communication between the cylinder bores and the discharge chamber, and on both sides of the valve plate, a suction valve sheet and a discharge valve sheet are arranged.
FIG. 11 typically illustrates the arrangement of a part of the rear end portion of the conventional multi-cylinder swash plate type compressor. That is, a valve plate 10 is arranged between the rear end of the cylinder block 1 and a rear housing 11. The valve plate 10 is attached to the rear end of the cylinder block 1 via a suction valve sheet 21 having suction valves 21a for openably closing suction ports 10a of the valve plate 10 and discharge apertures 21b aligned with discharge ports 10b of the valve plate 10. A discharge valve sheet 18 having a plurality of discharge valves for openably closing the discharge ports 10b of the valve plate 10 and a valve retainer 19 are attached to the outer end face of the valve plate 10 by a screw bolt. The refrigerant gas is drawn from a suction chamber 12 into each cylinder bore 4 through each suction port 10a of the valve plate 10 when each suction valve 21a is opened due to the pumping-in action of a piston 5 reciprocating within the corresponding cylinder bore 4. When the piston 5 carries out a compressing motion by moving toward the rear end of the cylinder block 1, the refrigerant gas is compressed within the cylinder bore 4 until a predetermined pressure level is reached. When the predetermined pressure level is reached, the compressed gas forcibly opens the discharge valve of the discharge valve sheet 18 by pushing the discharge valve toward the valve retainer 19 and is pumped out of the cylinder bore 4 into a discharge chamber 13 of the rear housing 11, via the discharge aperture 21b of the suction valve sheet 21 and the discharge port 10b of the valve plate 10. Since the actions of a suction and compression of the refrigerant gas are regularly repeated by the reciprocating motion of the multi-cylinder pistons 5, the flow of the compressed refrigerant gas pumped into the discharge chamber 13 of the rear housing 11 from the cylinder bores 4 includes a pulsation in the pressure thereof at a frequency corresponding to N.times.M (N indicates number of the cylinder bores 4, and M indicates number of rotations of the compressor), and causes vibration to occur at each discharge valve of the discharge valve sheet 18, thus generating noise. The same pulsation and vibration phenomena also appears at the front side of the compressor. At this stage, each discharge aperture 21b of the suction valve sheet 21 is formed so that it is larger than the corresponding discharge port 10b of the valve plate 10. Therefore, when each piston 5 carries out the compression stroke, the compressed refrigerant gas pumped out of the cylinder bores 4 flows through the discharge ports 10b of the valve plate 10 as a non-turbulent flow of gas, as illustrated in FIG. 11, and enters the discharge chamber 13 in the rear housing 11. On the other hand, at the initial, intermediate, and final stages of the compression stroke of the respective pistons 5, there is a change in the direction and the pressure of the compressed refrigerant gas pumped out of the respective cylinder bores 4, i.e., the strength of flow of the compressed refrigerant gas, and as a result, when the compressed refrigerant gas collides with the discharge valves, the discharge valves of the discharge valve sheet 18 in turn act to increase the strength of flow of the compressed refrigerant gas, due to the flexible characteristics of these discharge valves, and vibrate at a half-open position thereof, as illustrated by the broken line in FIG. 11. Consequently, the magnitude of the discharge pulsation in the pressure of the compressed refrigerant gas as well as the noise level due to vibration of the discharge valves of the discharge valve sheet 18 increases at a specified frequency pulsation band. According to experiments by the present inventors, it was confirmed that the magnitude of the discharge pulsation in the compressed refrigerant gas becomes particularly large at a frequency band of approximately 0.4 KHz, as shown in FIG. 4. It was further confirmed that the noise level becomes high due to a large vibration of the discharge valves at a pulsation frequency band of approximately 0.9 KHz, as shown in FIG. 5, or at a particular number of rotations of the compressor, i.e., at approximately 900, 2,000, and 3,600 r.p.m, as shown in FIG. 6.
U.S. Pat. No. 4,534,710 discloses damping chambers arranged adjacent to the suction and discharge ports for suppressing pulsation in suction and discharge pressure of the refrigerant gas. However, the damping chambers of this conventional compressor are arranged outside the compressor body, and thus, the overall height of such a conventional compressor is relatively high. Therefore, there is a need for an appropriate internally arranged construction capable of suppressing pulsation in the discharge pressure of the compressed refrigerant gas.